Hydrodesulfurization of heavy hydrocarbon oil with hydrogen presaturation

ABSTRACT

In the hydrogenation of residue-containing hydrocarbon oils, coke formation is suppressed by predissolving hydrogen in the oil at a temperature below 700* F. and carrying out the hydrogenation at a temperature above 700* F.

United States Patent Franz et al.

1151 3,657,112 51 Apr. 18, 1972 [54] HYDRODESULFURIZATION OF HEAVY HYDROCARBON OIL WITH HYDROGEN PRESATURATION [72] Inventors: William ,F. Franz, Gardiner; Howard V.

Hess, Glenham, both of NY.

[73] Assignee: Texaco Inc., New York, N.Y.

[22] Filed: June 22,1970

[21] Appl.No.: 48,465

[52] US. Cl ..208/2ll 511 1111.01 ..c10 23/00 [58] FieldotSearch ..208/211,21o,2 o9

' Primary Examiner-Delbert E. Gantz Assistant Examiner-G. J. Crasanakis Attorney-Thomas H. Whaiey, Carl G. Reis and Robert Knox, Jr.

' 57 ABSTRACT In the hydrogenation of residue-containing hydrocarbon oils, coke formation is suppressed by predissoiving hydrogen in the oil at a temperature below 700 F. and carrying out the hydrogenation at a temperature above 700 F.

6 Claims, No Drawings HYDRODESULFURIZATION F HEAVY HYDROCARBON 01]. WITH HYDROGEN PRESATURATION This invention relates to the hydrogenation of heavy hydrocarbon oils. More particularly, it is concerned with the desulfurization of hydrocarbon oils containing at least 1 percent Conradson Carbon Residue.

Reactions involving. the catalytic hydrogenation of light hydrocarbon oils are known and have been carried out frequently both experimentally'and commercially. Although recently there has, been considerable discussion regarding. the

removal of sulfur from heavy hydrocarbon fuels, installations for the practice of the catalytic hydrodesulfurization of heavy petroleumoils, although greatly desirable, have not received much commercial acceptance because of the rapiddeactivation rateof the catalyst. The commercial catalytic hydrodesulfurizationof light hydrocarbon oils such as naphthas has been practiced successfully for many yearsflhis is so because the catalyst requiresregeneration for the restoration of catalytic activity as infrequently as once every 12 or 15 months. Ordinarily: the catalyst is regenerated by removing the coke deposited thereon by a procedure which involves sweeping the reactor with an inert gas and then introducing into the catalytic reaction zonea gaseous mixture containing a relatively small amount of oxygen to prevent overheating-of the catalyst bed by the exothermic oxidation of the coke or carbon on the catalyst. Gradually, the oxygen content of the gas is increased while maintaining the temperature of the catalyst bed within the desired limits until essentially all of the coke or carbon has been removed as carbon dioxide. The reactor is then swept withan inert gas and the. on-stream period is resumed.

Unfortunately, in the catalytic hydrogenation of heavy residue-containing hydrocarbon oils not only is the catalyst rapidly deactivated by the deposition of coke thereon but, in

addition, metals, such as nickel, vanadium and iron. which also. have a detrimental effect on. its activityare deposited on the catalyst.

The particular problem involvedin the desulfurization or hydrogenation of heavy hydrocarbon-oils is that notonly is the catalyst deactivated rapidly by the deposition of coke thereon necessitating frequent regeneration but the regeneration of the' catalyst by oxidation of the coke does not removethe deposited metals. Thus, not only does thecatalyst become deactivated rapidly but, in addition, the ordinary type of oxidative regeneration does not restore the catalyst to a commercially practical activity.

In the hydrogenation of residual stocks the major part of-the hydrocarbon is in the liquid phase at the temperature and pressure of the reaction zone when conventional operating conditionsare used. This liquid phase hydrocarbon exists as a film over the catalyst particles indown-flow operations. In order for the. hydrogenation reaction to take place, hydrogen must first dissolve in the liquid from the gas phase and then diffuse through theliquid film to the catalyst surface before catalytic hydrogenation can begin. It follows that if the rate-of the hydrogen reaction is greater than the rate of hydrogen.

solution or diffusion, the reaction site at. the point. of contact between thecatalyst and the oil will be hydrogen deficient and consequently reactions. other than hydrogenation, such as cracking, which lead to the deposition of coke and the con-.

comitant deactivation of the catalyst will take place. However, if an amount of hydrogen at least equivalent to that required in the hydrogenation reaction can be predissolved in the liquid to provide a sufficient supply of hydrogen at the reaction site, undesired Vside reactions would, be'suppressed and the desired hydrogenation would be promoted.

According to our invention there is provided a process for the catalytic hydrogenation of heavy hydrocarbon oils containing at least 1 percent Conradson Carbon Residue which comprises passing said oil in intimate contact-with hydrogen through a presaturation zone at a temperaturebelow 700 F. and then contacting the liquid oil containing dissolved hydrogen with a hydrogenation catalyst in the presence of free hydrogen under hydrogenating. conditions. at a temperature above 700? F.

The charge stocks to which the process of the present invention may be applied include any hydrocarbon oilhaving a Conradson Carbon Residue of at least 1 percent for example atleast 5 percent or even 10 percent or higher such as atmospheric residua,.vacuum residua, heavy gas oils, shale oil, tar sand oil, crude petroleum oils, and the like. The charge stockis introduced into a presaturation zone where it is contacted with hydrogen under conditions to effect the solution of a substantialamount of hydrogen in the oil. In this respect, the term presaturation" is intended to mean presolution, such as occurs with the solution of a solute in a solvent as distinguished from chemical saturation where an unsaturated compound is hydrogenated to produce a chemically saturated compound. To effect the presaturation, the oil is brought into intimate contact with about 500-10,000 SCF hydrogen per barrel of oil 'at an elevated pressure such as 500-5,000 p.s.i.g. and a temperature below 700' F. preferably between 500 F and 700 F. This is done preferably by passing the oil and hydrogen over a bed of inert contact material whereby a large surface area of oil is exposed to contact with hydrogen. Advantageously, the pressure is the same as that of the hydrogenation zone. Although the prior art shows that hydrogen becomes increasingly soluble in hydrocarbons as the temperature is increased, it has been found unexpectedly that for the purpose of the present invention the temperature of the presaturation zone should be maintained below 700 F. although more hydrogen would be dissolved in the oil at higher temperatures. Suitably the contacting is carried out in the presence of a catalytically inert material which has a large surface-area. Such materials include ceramic packing material whose chief chemical constituent is alpha alumina containing minor amounts of silica.- Various grades of alumina ranging from the high surface area gamma type catalyst support grades to the relatively I low surface area alpha forms. Preferred packing is in the shape of Berl saddles or Raschig rings.

The oil-containing dissolved hydrogen is then brought into contact with a hydrogenation catalyst at a pressure between 500-5000 p.s.i.g., a temperature between 700 and-900 F., a space velocity between 0.1 and 10 volumes of oil per volume of catalyst per hour in the presence of between 500 and 20,000 standard cubic feet of free (as distinguished from dissolved) hydrogen per barrel of oil. Preferred conditions are temperatures-between 700 and 850 F. pressures between 1,000 and 2,000 p.s.i.g., space velocities between 0.25 and 1.5 and hydrogen rates between 600 and 10,000 standard cubic feet per barrel. Advantageously, the volume ratio of the presaturation zone to the hydrogenation zone is within the range of 5:1 to 1:1 preferably about 2:1.

The presaturation and hydrogenation zones may be in separate reactor vessels or within the same reactor vessel. It is also possible to carry out the presaturation by passing the oil upflow or downflow through the inert bed with the hydrogen flow either. cocurrent'with or countercurrent to the oil flow. Similarly, the flow of oil through the hydrogenation zone may be either upflow or downflow with cocurrent or countercurrent hydrogen flow.

In a preferred embodiment of the present invention the beds are containediwithin the same reactor vessel and the oil-is introduced at the top of the vessel and is passed downflow first through the presaturation zone containing a bed of Berl saddles and then downflow through the catalytic hydrogenation zone. Hydrogen is introduced at the bottom of the catalyst bed and also atthe bottom of the presaturation zone to flow upward countercurrently to the oil.

The catalyst used in the hydrogenation zone comprises a hydrogenating component impregnated on a substantially inert support, such as silica, alumina, magnesia or zirconia and mixtures thereof. The hydrogenating component may be a Group 8 metal or compound thereof, optionally used in conjunction with a Group 1 6 metal or compound thereof. Preferably, the Group 8 metal is presentin the catalyst in an amount between about 2 and 15 percent by weight of the catalyst composite and the Group 6 metal, if used, is present in an amount between about 5 and 30 percent. Preferred com- I binations are catalysts comprising 4- 8% nickel or cobalt and EXAMPLE I In this example the charge is an Arabian vacuum residuum having the following characteristics:

API Gravity 8.7 Sulfur, wt. 3.4 Nitrogen, wt. 1 0.28 Conradson Carbon Residue, wt.7 17.55 Metals (Ni,V,Fe) ppm 17,41,25

The apparatus in this example is a contact zone divided into two sections, an upper section containing inert packing in the form of one-quarter inch Berl saddles and a lower section containing a bed of hydrodesulfurization catalyst prepared to contain 3.3 percent nickel oxide and 15.8 percent molybdena supported on alumina, the upper to lower section volume ratio being 2:1. The hydrocarbon charge is introduced at the top of the apparatus to flow downwardly through the inert packing and then through the catalyst bed. Hydrogen is introduced at the bottom of the apparatus and also at the bottom of the inert packing to flow upwardly countercurrent to the downflowing charge.

Operating and other data appear below.

basis catalyst These data show that the desulfurization activity of the catalyst decreases on the average 12.5% per 100 hours onstream.

EXAMPLE ll This example is substantially a repeat of Example 1 with the exception that the temperature of the upper section containing the inert packing of Berl saddles is maintained below 700 F. The middle temperature recorded below is registered near the bottom of the inert packing.

TABLE 2 Time on stream, hours 60 156 Pressure, psig 1,500 1,500 1,500 Hydrogen rates, SCFB to catalyst 9,250 10,000 10,000

to inert packing 750 870 820 Temperature F Top 602 603 603 Middle 603 675 680 Bottom 748 748 752 Space velocity w/w/hr 0.69 0.69 0.71 Liquid Product wt. k charge 101.0 106.6 109.7 Sulfur wt% 2.0 2.1 2.2 7k Desulfurization 50.0 47.5 45.0

The above data show that when the presaturation temperature is maintained below 700 F. not only is the initial desulfurization activity of the catalyst higher, but in addition, its deactivation rate is lower, in the case of Example 11 being 3.5 percent per hours compared with 12.5 percent per 100 hours in Example I.

The present invention is also superior to prior art processes in that in known processes as the hydrogenation temperature of heavy oils increases so does the deactivation rate whereas, with our process, as the hydrogenation temperature is increased, there is a minimal increase in the catalyst deactivation rate with considerably improved desulfurization.

Other modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, and therefore, only such limitations should be imposed as are indicated in the appended claims.

1 claim:

1. A process for the catalytic hydrodesulfurization of a heavy hydrocarbon oil containing at least 1 percent Conradson Carbon Residue which comprises passing said hydrocarbon oil in intimate contact with hydrogen through a presaturation zone at a temperature between 500 F. and 700 F. and then contacting the oil substantially saturated with hydrogen with a hydrodesulfurization catalyst under desulfurization conditions and at a temperature above 700 F. and below 900 F.

2. The process of claim 1 in which the presaturation zone contains an inert packing.

3. The process of claim 2 in which the inert packing comprises alumina.

4. The process of claim 1 in which the pressure of the presaturation and desulfurization zones is between 500 and 5,000 p.s.i.g.

5. The process of claim 1 in which the heavy hydrocarbon oil is a residue-containing petroleum oil.

6. The process of claim 5 in which the heavy hydrocarbon oil contains at least 5 percent Conradson Carbon Residue. 

2. The process of claim 1 in which the presaturation zone contains an inert packing.
 3. The process of claim 2 in which the inert packing comprises alumina.
 4. The process of claim 1 in which the pressure of the presaturation and desulfurization zones is between 500 and 5,000 p.s.i.g.
 5. The process of claim 1 in which the heavy hydrocarbon oil is a residue-containing petroleum oil.
 6. The process of claim 5 in which the heavy hydrocarbon oil contains at least 5 percent Conradson Carbon Residue. 